A conductive-resin-coated steel pipe of about 28–32 mm in outer diameter is used as a frame component of a structure such as a flow-through rack, a driven conveyor or the like for holding or transporting parts of low electrical current devices or the like, in order to prevent static electrification. Thus, a coating of about 1 mm in thickness of conductive synthetic resin containing carbon black is formed on the outer circumferential surface of a thin-walled steel pipe of about 26–30 mm in outer diameter.
However, due to the use of carbon black, the above-mentioned conductive-resin-coated steel pipe has problems. That is, the use of carbon black makes the unit cost of the pipe expensive and makes the pipe black, which is not of pleasing appearance. Further, the carbon adheres to things that comes in contact with the pipe.
Taking these problems into consideration, the applicant has proposed a conductive-resin-coated steel pipe disclosed in Japanese Examined Utility Model Publication No. H8(1996)-5796, wherein on the outer circumferential surface of a thin-walled steel pipe, a coating of about 1 mm in thickness of synthetic resin such as AAS resin or the like of a chromatic color is formed, and on top of that coating a strip of conductive synthetic resin containing carbon black is formed integrally in the axial direction of the conductive-resin-coated steel pipe.
In this conductive-resin-coated steel pipe, the use of carbon black is reduced, which contributes to lowering the unit production cost.
Regarding the above-mentioned conductive-resin-coated steel pipe disclosed in Japanese Examined Utility Model Publication No. H8(1996)-5796, improvement in cost and appearance is acknowledged, to be sure, but conductive synthetic resin containing carbon black is still exposed although in the form of a strip. Therefore, the problem that the exposed carbon black adheres to things that come in contact with the pipe remains unsolved. Further, when an earth wire is to be connected to this pipe, it is necessary to pay attention to the position of a conductive portion. This causes another problem in that work efficiency is reduced.
In recent years, filler (fiber) having high impact resistance has been attracting attention. However, like the above-mentioned carbon black, the filler is expensive. Therefore, a steel pipe coated with resin containing the filler, particularly a steel pipe coated with conductive resin containing the filler has not been widely promoted.
Thus, the object of the present invention is to provide a conductive-resin-coated steel pipe in which filler is used in place of carbon black and which enables lower unit production cost and a better appearance, and a method of extrusion-forming such pipe.